1. Field of the Disclosure
The technology of the disclosure relates to fabricating gradient-index (GRIN) lenses. The GRIN lenses may be employed in fiber optic connectors for facilitating high communication bandwidth optical connections.
2. Technical Background
The increasing trend towards high performance computing (HPC) is driving the need for increased bandwidth of data communications between electrical data processing units. For example, communication rates between electrical data processing units may require data transfer rates of Gigabits per second (Gps) or even tens (10s) of Gps. In this regard, optical fibers are increasingly being used in lieu of copper wires as a communication medium between these electrical data processing units for high data rate communications. One or more optical fibers are packaged in a cable to provide a fiber optic cable for communicatively connecting electrical data processing units. Optical fiber is capable of transmitting an extremely large amount of bandwidth compared to a copper conductor with less loss and noise. An optical fiber is also lighter and smaller compared to a copper conductor having the same bandwidth capacity.
In this regard, fiber optic connectors are provided to facilitate optical connections with optical fibers for the transfer of light. For example, optical fibers can be optically connected to another optical device, such as a light-emitting diode (LED), laser diode, or opto-electronic device for light transfer. As another example, optical fibers can be optically connected to other optical fibers through mated fiber optic connectors. In any of these cases, it is important that the end face of an optically connected optical fiber be precisely aligned with the optical device or other optical fiber to avoid or reduce coupling loss. For example, the optical fiber is disposed through a ferrule that precisely locates the optical fiber with relation to the fiber optic connector housing.
It is common to provide flat end-faced multi-fiber ferrules to more easily facilitate multiple optical fiber connections between the fiber optic connector supporting the ferrule and other fiber optic connectors or other optical devices. In this regard, it is important that fiber optic connectors be designed to allow the end faces of the optical fibers disposed in the ferrule to be placed into contact or closely spaced with an optical device or other optical fiber for light transfer. If an air gap is disposed between the optical fiber and the optical device or other optical fiber, the end of the optical fiber is cleaved (e.g., laser-cleaved) and polished into a curved form to allow it to act as a lens. Spherical aberrations can occur when the end face of the optical fiber is cleaved and polished into a curved form, thereby introducing optical losses.
Gradient-index (GRIN) lenses offer an alternative to providing polished curvatures onto ends of optical fibers to form optical lenses. GRIN lenses focus light through a precisely controlled radial variation of the lens material's index of refraction from the optical axis to the edge of the lens. The internal structure of this index gradient can dramatically reduce the need for tightly controlled surface curvatures. This allows GRIN lenses to be provided with planar or substantially planar end surfaces or end faces to collimate light emitted from the optical fibers or to focus an incident beam into optical fibers.
A GRIN lens can be fabricated by cutting a portion of a GRIN rod to a desired length. For example, a mechanical cleaving process may be employed to cut a GRIN rod to the desired length as an initial step to fabricating a GRIN lens. As another example, a laser may be employed to cut a GRIN rod to the desired length to fabricate a GRIN lens. The process of cutting a GRIN rod to form a GRIN lens also creates end faces in the GRIN lens. The end faces of GRIN lenses can also be polished to be planar or substantially planar to a mating face. Mechanical polishing may be employed to polish the end faces of GRIN lenses. Mechanical polishing may be desired over laser polishing. Laser polishing may require exposing the GRIN lenses to laser energy for sufficient periods of time that may damage or crack the GRIN lenses. However, mechanical polishing processes can be labor-intensive. Mechanical polishing equipment can also be expensive and not have the desired manufacturing throughput. At various stages of polishing, the ferrules and respective optical fibers may also have to be inspected. Also, human involvement in mechanical polishing can lead to optical surface variations in mechanical polishing processes.